android.content.Context.getPackageName()' 在一个空对象引用上 [英] android.content.Context.getPackageName()' on a null object reference

问题描述

我正在使用实现接口的 Fragments.

I am working with Fragments which implements an interface.

public class SigninFragment extends Fragment implements SigninInterface 

fragment类中接口的方法实现如下

The interface's method implementation in the fragment class is as follows.

@Override
public void afterSubmitClicked(String userId, Bundle bundle) {

    Log.d(TAG,"Calling time afterSubmitClicked called"+bundle);
    
    if(!userId.equals("-1")){
        //Logged in successfully
        //Move to MusicHome
        
        Intent mIntent = new Intent(getActivity(),MusicHome.class);
        mIntent.putExtra("SigninFragment.user_details", bundle);
        startActivity(mIntent);
        
    }else{
        //Logging in failed
        //show error dialog
    }
    
}

在执行一个 AsynchronousTask(扩展 AsyncTask)类后调用该方法.

This method is called after exectuting a AsynchronousTask (which extends AsyncTask) class.

但我正在崩溃.并且错误信息显示

But I am getting crash. And the error message shows

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference

Logcat

   02-14 16:37:04.648: E/AndroidRuntime(28177): Process: com.raaga.android, PID: 28177
02-14 16:37:04.648: E/AndroidRuntime(28177): java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.content.ComponentName.<init>(ComponentName.java:77)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.content.Intent.<init>(Intent.java:3996)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at com.raaga.fragments.SigninFragment.afterSubmitClicked(SigninFragment.java:152)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at com.raaga.asynctask.SignInAsyncTask.onPostExecute(SignInAsyncTask.java:92)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at com.raaga.asynctask.SignInAsyncTask.onPostExecute(SignInAsyncTask.java:1)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.os.AsyncTask.finish(AsyncTask.java:632)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.os.AsyncTask.access$600(AsyncTask.java:177)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.os.Handler.dispatchMessage(Handler.java:102)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.os.Looper.loop(Looper.java:135)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at android.app.ActivityThread.main(ActivityThread.java:5221)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at java.lang.reflect.Method.invoke(Native Method)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at java.lang.reflect.Method.invoke(Method.java:372)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
02-14 16:37:04.648: E/AndroidRuntime(28177):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

推荐答案

我发现了我所做的错误.我们需要从覆盖方法 OnAttach() 中获取活动实例例如，

I have found the mistake what I did. We need to get the activity instance from the override method OnAttach() For example,

public MainActivity activity;

@Override
public void onAttach(Activity activity){
    this.activity = activity;
}

然后将活动作为上下文传递，如下所示.

Then pass the activity as context as following.

Intent mIntent = new Intent(activity, MusicHome.class);

这篇关于android.content.Context.getPackageName()' 在一个空对象引用上的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！